This invention relates to an antenna unit and, in particular, to an antenna unit using an EBG (Electromagnetic Band Gap) reflector.
As one of antenna units, a monofilar spiral array antenna is proposed in article which is contributed by Hisamatsu Nakano et al to Int. Symp. Antennas and Propagation (ISAP), pages 629-632, Soul, Korea, August 2005, and which has a title of “A monofilar spiral antenna array above an EBG reflector.” In the manner which will later be described in conjunction with FIGS. 1 through 3, the monofilar spiral array antenna disclosed in the article comprises a mushroom-like EBG reflector and first through fourth array elements which are spaced with an array distance in the x-direction. The first through the fourth array elements are backed by the mushroom-like EBG reflector. Each array element is composed of one vertical filament and N horizontal filaments. Each array element is called a curl antenna. The mushroom-like EBG reflector is composed of (Nx×Ny) square patches. At any rate, this article reports gain enhancement of curl antennas by using array technique.
However, it is necessary for the monofilar spiral array antenna to arrange, as an antenna device, a plurality of curl antennas in an array fashion. Therefore, the monofilar spiral array antenna is disadvantageous in that a feeding method is complicated.